You type in two choices and it comes back and tells you which of the two is more common:

I wouldn’t recommend it as a grammar checker as it would just take far too long – but it might be useful for learners struggling with phrasal verbs or idiomatic expressions.

Also – it could be a fun research tool to use in class as a way of raising learners awareness of common errors – give the learners a list of pairs of expressions, some of which could be unfortunate utterances taken from past classes or written work, and the learners discuss and choose which they think is more common / correct, before checking on the website.